Marine mammals, such as seals, sea lions, or porpoise are being utilized to perform work functions in the ocean waters. These mammals have been utilized for enabling the retrieval of objects located on the ocean bottom. This has been accomplished by mounting a tethered device to the mammal which can be carried by the mammals to the object and clamped thereto, so that personnel on a surface ship can utilize the tether to retrieve the object. One of the problems with these marine mammals is that while performing the work function or while being trained to perform such work functions in the open ocean, they will decide to escape or will undertake a long hunting trip for food. The previous method of preventing such problems has been to attach a line to the mammal so that he can be returned to the trainers. However, this line has seriously encumbered the mammal's swimming ability, and also endangers the mammals life by the possibility of becoming entangled with underwater objects. A better way of ensuring the return of these worker mammals is needed.